1. Field of the Invention
This invention relates to a process for preparing polyisobutylene oxide moldings. More particularly, the invention relates to a process for preparing polyisobutylene oxide moldings which comprises the step of quickly cooling a heated or molten resin of polyisobutylene oxide to obtain crystalline resin different from that obtained by slow cooling, thereby facilitating the subsequent processing operations, such as stretching.
2. Description of the Prior Art
Although polyisobutylene oxides are highly crystalline polymers having excellent physical properties, the presently available films and thin sheets of polyisobutylene oxide do not have sufficient transparency or satisfactory mechanical properties.
It has been already known that remarkable improvements in strength, transparency, bending strength and impact strength are attained by subjecting polyisobutylene oxide moldings to a stretching treatment on heating or another heat treatment thereby stretching them to several or several tens times their original size and that the resulting films are practical (see the Official Gazette of Japanese Pat. Publication No. 12180/1965).
However, if the polyisobutylene oxide moldings are subjected to tensile drawing, particularly for the purpose of obtaining films, they must be heated to a temperature around their melting points (170.degree.-175.degree.C), because they are highly crystalline polymers. Consequently, even if there occurs only a small error in the temperature, partial fusion of the polymer can occur if the temperature is even slightly too high or the drawing operation per se can become very difficult if the temperature is even slightly too low due to insufficient softening, thereby causing breakage of the film during the drawing operation. Small errors or fluctuations in the temperature or the thickness of the sheet cause remarkable unevenness in the thickness of the stretched film. Thus, precisely controlled conditions are required for the production of the sheets on a commercial scale.
For facilitating the tensile stretching, a method can be considered in which heat rolls are used. However, this method is not suitable for obtaining a thin, transparent film on a commercial scale. The stretching property can be improved by means of copolymerization, blending or incorporation of an additive in the polyisobutylene oxide resin. However, these technical means are not preferred, because by these means, the physical properties of the resulting film are changed.